270
FXUS62 KRAH 181938
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
240 PM EST WED DEC 18 2024
SYNOPSIS
AN UPPER LEVEL DISTURBANCE OVER THE MISSISSIPPI VALLEY WILL SHIFT
EASTWARD OVER THE SOUTHEAST STATES AND CAROLINAS THROUGH EARLY
THURSDAY, DRAGGING A STRONG SURFACE COLD FRONT ACROSS THE AREA. A
COOLER AIR MASS WILL BUILD IN LATE THURSDAY THROUGH FRIDAY, THEN A
SECOND COLD FRONT AND UPPER LEVEL DISTURBANCE WILL MOVE THROUGH
FRIDAY NIGHT, BRINGING ARCTIC AIR INTO THE REGION FOR THE WEEKEND.
NEAR TERM /THROUGH TONIGHT/
AS OF 1025 AM WEDNESDAY...
* DENSE FOG ADVISORY WAS ALLOWED TO EXPIRE AS CONDITIONS BEGIN
TO IMPROVE ALTHOUGH PATCHES OF THICK FOG WILL BE SLOW TO
COMPLETELY ERODE ACROSS THE SANDHILLS AND SOUTHERN COASTAL
PLAIN.
QUICK UPDATE THIS MORNING AS WIDESPREAD DENSE FOG EARLY THIS
MORNING IS BEGINNING TO ERODE ALTHOUGH SOME AREAS OF FOG WILL
PERSIST THROUGH MIDDAY. FOG WILL BE MOST STUBBORN AND PERSISTENT
ACROSS SOUTHERN AND SOUTHEASTERN AREAS IN THE SANDHILLS AND
SOUTHERN COASTAL PLAIN WHERE VISIBILITIES MAY BE LESS THAN A 1/2
MILE AT TIMES THROUGH MIDDAY. IN THESE AREAS A LAYER OF STRATUS
AND EVEN A FEW SPRINKLES MOVING NORTHEAST OUT OF NORTHEASTERN
SC MAY PROVIDE COVER AND REDUCE THE AMOUNT OF SUNSHINE AVAILABLE
TO ERODE THE FOG. ADDED A SLIGHT CHANCE OF A SHOWER ACROSS
SOUTHEASTERN AREAS LATE THIS MORNING AND EARLY THIS AFTERNOON AS
WARM ADVECTION SPRINKLES/SHOWERS SPREAD INTO THE SANDHILLS AND
COASTAL PLAIN. MADE LITTLE ADJUSTMENT TO TEMPERATURES WHICH WILL
BE A WILD RIDE TODAY DEPENDING ON FOG AND CLOUD COVER WITH THE
POTENTIAL FOR TEMPS TO BE TOO WARM ACROSS THE SOUTHEASTERN
AREAS. -BLAES
PREVIOUS DISCUSSION FROM 310 AM...
AS OF EARLY THIS MORNING, DENSE FOG IS PRIMARILY CONTAINED TO
NORTHERN AND SOUTHERN COUNTIES, WITH VISIBILITIES STILL 5-10 MILES
ACROSS CENTRAL COUNTIES, BUT MODEL GUIDANCE INDICATES THAT AREAS OF
DENSE FOG ARE LIKELY ACROSS THE ENTIRE FORECAST AREA BY SUNRISE.
THEREFORE, HAVE ISSUED A DENSE FOG ADVISORY THROUGH MID-MORNING.
LOW PRESSURE IS CURRENTLY ACROSS WESTERN KENTUCKY AND WILL
CONTINUE TO MOVE NORTHEAST THROUGH THE DAY, REACHING THE NEW
YORK CITY METRO AREA BY THIS EVENING AND MOVING EAST OF MAINE BY
THURSDAY MORNING. HIGH-RESOLUTION GUIDANCE SUGGESTS THAT THERE
COULD BE SOME SPOTTY SHOWERS THROUGH MUCH OF THE DAY, BUT DO NOT
SEE MUCH OF A FORCING MECHANISM IN PLACE ACROSS THE REGION.
HAVE KEPT THE FORECAST DRY THIS MORNING, THEN HAVE POPS BEGIN TO
INCREASE FROM BOTH NORTHWEST AND SOUTHEAST ACROSS THE AREA. THE
COLD FRONT APPROACHING THE REGION FROM THE NORTHWEST WILL BRING
A HIGHER POTENTIAL FOR RAINFALL, BUT ACROSS THE SOUTHEAST,
THERE WILL BE GREATER INSTABILITY, AT LEAST 500 J/KG OF MUCAPE,
AND WILL HAVE A CHANCE OF THUNDERSTORMS ACROSS THE SOUTHEAST
LATE THIS AFTERNOON INTO TONIGHT. THINK THAT THE HIGHEST CHANCE
FOR SHOWERS WILL COME LATE THIS EVENING, AND BELIEVE THAT THE
BULK OF THE RAINFALL WILL OCCUR EAST OF THE TRIAD. RAINFALL
TOTALS CONTINUE TO COME DOWN - OUTSIDE OF AN ISOLATED HEAVY
SHOWER/THUNDERSTORM, MOST LOCATIONS WON'T RECEIVE MORE THAN A
TENTH OF AN INCH OF RAIN. MODELS HAVE REMAINED CONSISTENT IN
PUSHING ALL THE RAIN TO THE EAST OF THE REGION BY DAYBREAK.
ANOTHER UNSEASONABLY WARM DAY IS EXPECTED, WITH HIGHS RANGING
FROM THE MID 60S NEAR THE VIRGINIA BORDER TO THE MID 70S ACROSS
THE SOUTH. THERE WILL BE A WIDE RANGE OF OVERNIGHT LOWS WITH THE
COLD AIR NOT IMMEDIATELY ARRIVING EVERYWHERE BEHIND THE FRONTAL
PASSAGE - LOCATIONS IN THE NORTHWEST WILL FALL INTO THE LOWER
40S, WHILE IN THE SOUTHEAST, TEMPERATURES WILL ONLY FALL INTO
THE MID 50S.
SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/
AS OF 240 PM WEDNESDAY...
THE MAIN STORIES FOR THIS PERIOD WILL BE THE POTENT UPPER PV MAX
THAT CROSSES THE CAROLINAS FRI AFTN/NIGHT, FOLLOWED BY THE ARRIVAL
OF ARCTIC AIR.
THU/THU NIGHT: THE SURFACE COLD FRONT IS EXPECTED TO BE SE OF THE
FORECAST AREA BY DAYBREAK THU, HOWEVER THE NORTHERN PORTIONS OF THE
SOUTHERN STREAM SHORTWAVE TROUGH WILL BE OVERHEAD, SHIFTING
EASTWARD, AND THERE MAY BE SUFFICIENT LOW LEVEL (ESP 925-850 MB)
MOISTURE DESPITE THE INCREASING LOW LEVEL STABILITY TO SQUEEZE OUT
ISOLATED PATCHES OF VERY LIGHT RAIN OR DRIZZLE IN THE E EARLY THU
MORNING. ANY BRIEF FAIR SKIES ARE LIKELY TO FILL IN WITH STRATOCU IN
THE AFTN AS MOIST UPGLIDE AT 285-290K RAMPS UP OVER ALL BUT OUR
EXTREME W AND BECOMES TRAPPED WITHIN THE LOWER REACHES OF THE STABLE
LAYER EVIDENT FROM 925-800 MB. WITH DECENT MIXING IN THE LOWEST 50
MB, HOWEVER, WE SHOULD SEE A FEW GUSTS IN THE MORNING THROUGH EARLY
AFTN, UNTIL THE LOW LEVEL PRESSURE GRADIENT RELAXES. EXPECT HIGHS IN
THE 50S, NEAR TO A DEGREE OR SO ABOVE NORMAL, AS THE INCOMING AIR
MASS WILL BE RELATIVELY MILD WITH ABOVE-CLIMO LOW LEVEL THICKNESSES.
WITH NOCTURNAL STABILIZATION AT THE SURFACE THU NIGHT RESULTING IN A
DEEP STABLE LAYER WITH WEAK WINDS INHIBITING ANY MIXING AND
DISPERSION OF THIS MOISTURE JUST ALOFT, SKIES ARE LIKELY TO REMAIN
MOSTLY CLOUDY TO CLOUDY THROUGH THE NIGHT, AS SURFACE HIGH PRESSURE
RIDGING EXTENDS WEAKLY ACROSS THE AREA FROM THE NE. THESE CLOUDS
WILL HELP KEEP LOWS AT OR ABOVE NORMAL, IN THE 30S.
FRI-FRI NIGHT: A STRONG SHORTWAVE TROUGH NOW OVER THE PACNW WILL
TRACK SE THROUGH THE MIDWEST THROUGH THU AND, WITH THE ADDED PUNCH
OF A SERIES OF SHEARED VORTICITY STREAKS SWINGING THROUGH ITS BASE,
WILL MOVE THROUGH NC FRI AFTN/EVENING, ACCOMPANIED BY AN ARCTIC
SURFACE COLD FRONT. INCREASING LOW LEVEL WSW AND W FLOW FRI MORNING
SHOULD HELP SCOUR OUT THE STRATOCU OVER THE AREA FROM SW TO NE,
RESULTING IN A PERIOD OF FAIR SKIES, ALTHOUGH THIS WILL QUICKLY GIVE
WAY TO INCREASING CLOUDS ONCE AGAIN. WITH A TROP FOLD LIKELY AND THE
TROPOPAUSE DIPPING TO BELOW 500 MB, A STEEPENING OF LAPSE RATES
BELOW 600 MB IS EXPECTED, ALONG WITH A MOISTENING OF THE LOW LEVEL
COLUMN. A CHANCE OF SHOWERS IS STILL EXPECTED LATE FRI INTO FRI
NIGHT. WHILE THE PROJECTED ELEVATED/SHALLOW CAPE IS QUITE SMALL,
GIVEN THE STRONG PV MAX AND THE ANTICIPATED MOISTENING UP INTO THE
MIXED PHASE REGION ALOFT, A FEW LIGHTNING STRIKES ARE POSSIBLE. THE
ARCTIC FRONT WILL PUSH ESE AND OFFSHORE FRI NIGHT, RESULTING IN
CLEARING W TO E OVERNIGHT, AND A PERIOD OF GUSTY WINDS IS POSSIBLE.
HIGHS IN THE UPPER 40S TO MID 50S, FOLLOWED BY LOWS FROM THE UPPER
20S TO MID 30S.
SAT/SAT NIGHT: THE POTENT SHORTWAVE TROUGH WILL HAVE PUSHED WELL
OFFSHORE, INDUCING MID LEVEL SUBSIDENCE, BUT WE'LL REMAIN WITHIN A
LONGWAVE MID LEVEL TROUGH EXTENDING DOWN THROUGH E NOAM SAT/SAT
NIGHT. MINOR PERTURBATIONS (WITH LOW INDIVIDUAL PREDICTABILITY) ARE
LIKELY TO SWING THROUGH THE REGION WITHIN BROADLY CYCLONIC WNW FLOW,
BUT WITH DEEP MOISTURE LACKING, WE SHOULD SEE LITTLE MORE THAN SOME
HIGH CLOUDINESS (PERHAPS OROGRAPHICALLY ENHANCED ACROSS OUR N AND
INTO VA) TOPPING SOME HIGH-BASED FLAT AFTN CU THAT WILL FORM WITH
MIXING. THE TIGHT POST-FRONT MSLP GRADIENT SAT MORNING WILL
RESULTING IN A CHILLY NW BREEZE EARLY IN THE DAY, WITH WINDS
LIGHTENING LATE AS THAT GRADIENT RELAXES. EXPECT HIGHS IN THE 40S,
AND LOWS IN THE UPPER TEENS TO MID 20S. -GIH
LONG TERM /FRIDAY THROUGH TUESDAY/
AS OF 230 AM WEDNESDAY...
THE STRONG TROUGH FROM THU NIGHT IS FORECAST TO STRENGTHEN AS IT
MOVES ACROSS OUR REGION FRI AFTERNOON AND EVENING. MUCH OF THE 00Z
SUITE OF THE GFS/CMC/ECMWF ARE IN VERY GOOD AGREEMENT WITH THE TRACK
AND TIMING OF THE VORT MAX MOVING SOUTHEAST. THE VORT MAX IS LARGELY
FORECAST TO MOVE DIRECTLY OVERHEAD CENTRAL NC CENTERED AROUND EARLY
EVENING, WITH IMPRESSIVE 180+ M HEIGHT FALLS. THERE IS A CHANCE OF
SOME LIGHT RAIN OR DRIZZLE EAST OF US-1 FRI MORNING TO EARLY
AFTERNOON ASSOCIATED WITH LOW-LEVEL ISENTROPIC ASCENT ATOP THE
SURFACE WEDGE. HOWEVER, FEEL THE BETTER CHANCE OF LIGHT RAIN WILL BE
LATE FRI AFTN AND EVENING WITH THE VORT MAX. MODELS ALSO SHOW A
SURFACE TROUGH AXIS AND PERHAPS A WEAK SURFACE LOW ALONG SC,
TRACKING SE WITH THE MID-LEVEL VORT MAXIMA. ENSEMBLE GUIDANCE WAS
ALSO TRENDING WITH HIGHER POP CHANCES. WE RAISED POPS ACCORDINGLY
(30-PERCENT) IN THE LATE AFTN/EVE AREA-WIDE EXCEPT THE FAR SOUTHERN
PIEDMONT. HIGHS FRI IN THE LOW/MID 50S. IT LOOKS LIKE THE VORT MAX
MOVES EAST BEFORE THE MUCH COLDER AIR MOVES IN. MODEL SOUNDINGS AND
PTYPE NOMOGRAMS ALSO SHOW THIS, SUCH THAT ANY PTYPE CONCERNS ARE NOT
ANTICIPATED THUS FAR.
IT IS ALL ABOUT MUCH COLDER AIR SAT TO EARLY NEXT WEEK AS COLD HIGH
PRESSURE OVER THE UPPER MS VALLEY SAT EVENTUALLY SETTLES INTO THE
MID-ATLANTIC COME MONDAY. AN ARCTIC FRONT WILL MOVE THROUGH SAT
NIGHT. LOW-LEVEL THICKNESSES BECOMING LOWEST SUN INTO MON AROUND
1265-1270 M, SOME 40-45 M BELOW AVERAGE. ANOTHER VORT MAX IS
FORECAST IN THE GUIDANCE/ENSEMBLES TO MOVE THROUGH LATE SAT INTO SUN
WITH THE NW FLOW ALOFT, BUT CURRENT INDICATIONS POINT TO A FURTHER
SOUTH AND WEST TRACK SUCH THAT WE KEPT THE FORECAST DRY FOR NOW.
HIGHS SAT WILL FALL FURTHER INTO THE LOW TO MID/UPPER 40S. HIGHS
SUN/MON WILL BE SOME 12-16 DEGREES BELOW AVERAGE IN THE UPPER 30S TO
LOW 40S AND LOWS IN THE MID TEENS TO LOW 20S, COLDEST MON MORNING
UNDER THE ANOMALOUSLY STRONG 1040 MB SURFACE HIGH.
ENSEMBLE DATA SHOWS THAT RIDGING TO QUASI-ZONAL FLOW IS FORECAST TO
BUILD IN MON AND TUE AT MID-LEVELS, WHILE THE COLD SURFACE HIGH
SLOWLY RETREATS NORTHWARD. THIS SHOULD FAVOR WARMER HIGHS BY TUE IN
THE MID 40S TO LOW 50S.
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
AS OF 225 PM WEDNESDAY...
24 HOUR TAF PERIOD: WIDESPREAD IFR AND LIFR FOG AND STRATUS ACROSS
CENTRAL NC EARLY THIS MORNING HAS ERODED AND LIFTED WITH AREAS OF
MAINLY MVFR AND ISOLATED IFR STRATUS ACROSS THE AREA, ESPECIALLY
FROM RALEIGH SOUTH AND EAST. ADDITIONAL IMPROVEMENT IN SKY
CONDITIONS IS LIKELY TO CONTINUE INTO THE AFTERNOON WITH VFR TO MVFR
CONDITIONS EXPECTED WITH AREAS OF STRATOCUMULUS WITH BASES OF 2.5 TO
4 KFT.
A COLD FRONT AND MID/UPPER LEVEL TROUGH WILL APPROACH FROM THE WEST
AND MOVE ACROSS THE AREA TONIGHT AND EARLY THURSDAY PRODUCING WIDELY
SCATTERED SHOWERS THAT WILL SHIFT EAST THIS EVENING INTO THE
OVERNIGHT. THE GREATEST CHANCE OF SHOWERS WILL BE BETWEEN 00Z AND
06Z WITH THE GREATEST THREAT ALONG WITH A SMALL CHANCE OF A
THUNDERSTORM ACROSS EASTERN LOCATIONS INCLUDING THE COASTAL PLAIN
AND SANDHILLS INCLUDING THE KFAY AND KRWI TERMINALS. GIVEN LIMITED
COVERAGE AND CONFIDENCE WILL OMIT A MENTION OF THUNDER IN THE TAFS.
SHOWERS WILL PRODUCE LOCAL CIG AND POSSIBLY VSBY RESTRICTIONS.
SOUTHWEST WINDS AT 6 TO 12 KTS WILL GUST TO AROUND 20KTS THIS
AFTERNOON. THE FRONT WILL MOVE THROUGH THE AREA FROM WEST TO EAST
BETWEEN 05 AND 10Z AND WILL BE ACCOMPANIED BY A WIND SHIFT TO THE
NORTHWEST WITH AN AREA OF LOW STRATUS DEVELOPING LATE TONIGHT ACROSS
THE COASTAL PLAIN AND SANDHILLS INCLUDING THE KFAY AND KRWI
TERMINALS. CONSIDERABLE CLOUDINESS IS EXPECTED ON THURSDAY WITH CIGS
OF 2-4KFT RESULTING IN SOME MVFR RESTRICTIONS DURING THE DAY,
ESPECIALLY SOUTH AND EAST OF RALEIGH. NORTHWEST WINDS WILL BECOME
NORTHEASTERLY AT AROUND 10KTS WITH SOME GUSTS TO AROUND 15KTS.
OUTLOOK: ANOTHER WEATHER SYSTEM WILL BRINGING A CHANCE OF SHOWERS
AND A THREAT OF SOME MVFR RESTRICTIONS ON FRIDAY. BEHIND THIS
SYSTEM, COLD ARCTIC AIR WILL SPREAD INTO THE REGION ACCOMPANIED BY
GUSTY NORTHWEST WINDS FRIDAY NIGHT AND SATURDAY. FAIR WEATHER IS
EXPECTED FOR SUNDAY AND MONDAY. -BLAES
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...HARTFIELD
NEAR TERM...BLAES/GREEN
SHORT TERM...HARTFIELD
LONG TERM...KREN
AVIATION...BLAES
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